Positive-Tone Polymer Images by Surface Modification in Ion Beam Exposures

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Abstract
Under exposures of high energy radiation in vacuum, decarboxylation takes place efficiently on polymer surfaces having carboxylic acid groups. Low energy electron and ion beams are particularly efficient in these chemical reactions on the surfaces because their energy deposition is limited to very shallow depths. The surface areas exposed to the radiation have properties similar to hydrocarbons after decarboxylation, resulting in non-reactions in gas phase silylation, while unexposed areas undergo silylation readily due to the presence of reactive acid groups. The non-silylated areas etch faster in oxygen reactive ion etchings, giving rise to positive tone polymer images. Polymers like poly(methacrylic acid), poly(acrylic acid), and their copolymers have been used. Other polymers like poly(styrene), poly(chloromethylstyrene), and Novolac resins can also be used, because these polymers readily undergo photo-oxidation under uv-irradiation in air, generating carboxylic acid groups on their surfaces.

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